The present invention generally relates to vehicle recovery devices with masts and booms (“vehicle wreckers”), including those that can be rotated (“rotating wreckers”), as well as those which cannot be rotated, and whose supporting travel base can be moved along the longitudinal axis of the wrecker, to increase the reach of the boom. Such vehicle wreckers allow a load to be lifted and then moved a given distance forward or rearward along the wrecker longitudinal axis.
With prior art vehicle wreckers such as the NRC Slider and the Miller XLT Traveler, the wrecker mast and boom move along travel frame tubes on Nylatron® or bronze bearing pads. A drawback to this type of system, the former of which has been used for more than 20 years, is that it is affected greatly by the combination of the load applied to the boom, the size of the travel cylinder, and the resulting friction between the bearing pads and the travel tubes. With these prior art systems, lubrication between the bearing pads and the travel tubes is critical. As the load increases on the boom, the need for lubrication increases. Also, as the load on the boom increases, the ability to maintain sufficient lubrication between the bearing pads and travel tubes becomes increasingly more difficult. Operators utilize personal preferences for lubrication choices. The lubricants used range from differing types of grease, to paraffin-based automotive undercoating, both applied with a brush, to spray-on motorcycle chain grease. No matter which lubricant is used, they only work for a short period of time. Whether it is the lubricant being wiped off in use, dried by the sun or washed off by weather, they all have a short lifespan. In many cases, if the travel tubes are not lubricated before a load is applied to the boom, it is impossible to move the load. In this case, the load must be lowered and disconnected so that the travel tubes can be properly lubricated. The load may then be reconnected, and the travel function operated. This problem seems to be something that most operators have resigned themselves to and live with.
Over the years, various attempts have been made to solve these problems. The size of the travel cylinder was increased, which provided some advantage. Installing an automatic greasing system was tried, to eliminate the need to climb onto the machine and brush grease on the travel tube. This system appeared to work in theory, but was not usable in reality. Different bearing materials have been tried, and attempts have been made to come up with other ways to distribute the loads over a larger area; however, no advantageous solution was found.
During brainstorming sessions, the concept of using a wheel instead of bearing pads was discussed. This would eliminate the friction that the bearing pad sees, but wheels have their own drawbacks. Unlike bearing pads with a larger area to distribute the load, wheels have only a small contact line along the width of the wheel. This will cause high compressive loads along this contact line. To compensate for this, additional wheels may be added which will help, but will not completely solve the load distribution problem. If enough wheels can be added, the next problem is to design an axle that is large enough to carry the load without bending. However, these designs yielded systems that were too large to fit into the given area available. In sum, there is agreement within the industry that a solution to these problems would be advantageous.
In addition to solving the above-mentioned problems, there is also a need to provide a vehicle wrecker having certain advantages. For example, there is a need to provide a vehicle wrecker with a movable travel base to provide increased reach and working area for the mast and boom. There is also a need to provide a vehicle wrecker with the ability to lift a heavy load close to the rear of the wrecker, and then move it a distance away from the rear of the wrecker without having to reposition the boom. There is a further need to provide a vehicle wrecker with the ability to lift a heavy load at the rear of the wrecker, and then rotate it around the rear corner of the wrecker without the need for repositioning the boom. There is also a need to provide a vehicle wrecker than can lift a load on one side of the wrecker and then travel to the rear, rotate the load around the rear corners of the wrecker, and then travel forward without the need to reposition the boom. Still further, there is a need to provide a vehicle wrecker with an increased lifting capacity such that the wrecker, by traveling the load toward or away from the rear of the wrecker, can move the boom into a better position to lift at its rate range. Additionally, there is a need to increase the lifting capacity of a vehicle wrecker by enabling movement of the load toward the rear of the wrecker, thus moving the counterweight of the engine further away from the load being lifted.